Fabrication Of Colloidal Crystals And Their Application In Information Displays

Structural colors of photonic crystals usually come from the interactions between their internal microstructures and light. Because these physical colors are highly saturated and ultra-stable, they have attracted much attention in many fields, such as sensors and displays. However, due to the Bragg diffraction, the colors usually appear different when observed from different viewing angles. Thus, the application of these structural colors could be greatly restricted, especially in wide viewing angle usages. A lot of efforts have been made to eliminate the iridescence of structural colors. Recently researchers made some progress in self-assembled colloidal crystals by introducing quasi-amorphous structures into the ordered colloidal arrays. The iridescence of colloidal crystals can be suppressed as the stray light is enhanced by the disorder microstructures. However, the quality of structural colors (i.e. color hue and saturation) is largely destroyed and the reflectivity of materials is suppressed. Moreover, the fabrication of quasi-amorphous materials is complex and not suitable for mass production. In this thesis we will introduce a new method to increase the viewing angles. We found that the symmetries in spherical colloidal crystals or their derivatives can eliminate the iridescent phenomenon and retain the color quality. Based on this method, we developed a series of colloidal crystal materials with wide viewing angles and demonstrated their applications in information displays. The detailed work is as follow:(1) A gravity-driven microfluidic device with online drying component was designed and constructed for mass generation of spherical colloidal crystals. The facts that affect microsphere’s surface morphology, size, monodisperse, stability were well studied and optimized. Under the optimized conditions, a series of high quality colloidal crystal beads were generated for the next experiments. This work helps to scale-up the yield and makes it possible for the microspheres to be widely used.(2) It was found that colloidal crystal beads with diameters of 50-300 μm have constant structural colors when observed from different viewing angles, and the hypothesis that spherical symmetry could eliminate iridescent colors was brought up and verified. It was also confirmed that colloidal crystal films composed of colloidal crystal beads and their inverse structures have similar wide viewing angle property. At last, the concept of photonic paper was demonstrated based on these colloidal crystal films. This work reveals that spherical symmetry could eliminate the iridescence of photonic crystals and offers new solutions to suppress iridescent colors.(3) By employing soft template and fast UV polymerization techniques, various colloidal crystal materials with symmetry surface morphologies were fabricated. It was proved that these non-spherical symmetries can also make angle-independent structural colors. This work further verified that symmetries could eliminate iridescent effect in photonic crystals and expand the scope of angle-independent colloidal crystal materials.(4) A simple electrophoretic display device was fabricated based on the principle of tunable photonic crystals. The surface of colloidal nanoparticles was chemically functionalized to enhance the stability of the electrophoretic liquid. The threshold voltage, response time and color gamut were well studied. This work demonstrated colloidal crystals could be employed in dynamic colorful displays.